1. Field of the Invention
The present invention relates to nonreciprocal circuit devices, such as isolators and circulators, and to a method of fabricating the same. More particularly, the invention relates to a nonreciprocal circuit device in which a plurality of components are integrated and a method of fabricating the same.
2. Description of the Related Art
Various types of isolators and circulators have been disclosed as high-frequency nonreciprocal circuit devices. An example of a conventional isolator will be described with reference to FIGS. 7 and 8.
In the fabrication process of an isolator, a plurality of central conductors 52 to 54 are placed on the upper surface of a ferrite substrate 51. The central conductors 52 to 54 intersect each other in the center while being electrically insulated from each other.
The integrated structure in which the central conductors 52 to 54 intersect each other is referred to as xe2x80x9ca netxe2x80x9d. A permanent-magnet plate 55 is deposited on the ferrite substrate 51 with the net therebetween. Capacitors 56a to 56c and a resistor 57 are also mounted so as to be electrically connected to the central conductors 52 to 54. The capacitors 56a to 56c and the resistor 57 may be disposed in various manners. After the components shown in FIG. 7 are assembled, the integrated unit is contained in a base 58 shown in FIG. 8. A magnetic cap 59 coated with a conductive film is placed on the base 58. A yoke 60 composed of a metal plate or the like is also mounted so as to be magnetically coupled to the cap 59.
As described above, with respect to the conventional isolator, many components must be prepared and assembled, resulting in difficulty in improving productivity and reliability.
Consequently, various attempts have been made to integrate a plurality of components constituting a nonreciprocal circuit device.
For example, Japanese Unexamined Patent Application Publication No. 8-222912 discloses a nonreciprocal circuit device using a sintered compact formed by integrally firing a laminate in which a green sheet for a magnetic member and a green sheet for a permanent magnet are laminated with a central conductor therebetween. The central conductor, the magnetic member, and the permanent magnet are formed into a single sintered compact using an integrating firing technique. The sintered compact is provided with a recess for receiving a magnetic yoke.
Japanese Unexamined Patent Application Publication No. 8-330812 discloses a method of fabricating a lumped-constant circulator, in which ferrimagnetic thin plates provided with central conductors printed thereon are laminated, and the resulting laminate is cut off, followed by firing. That is, the individual laminates, each corresponding to a lumped-constant circulator unit, are separated from a mother laminate, and by firing the laminates, structures in which central conductors and magnetic members are integrated are obtained.
Japanese Unexamined Patent Application Publication No. 9-326606 discloses a nonreciprocal circuit device in which a central conductor and capacitor electrodes constituting a capacitor are disposed within a sintered compact composed of a magnetic material.
As described above, various types of structure, in which a plurality of components of a nonreciprocal circuit device are integrated using an integrating firing technique or the like, have been disclosed. However, with respect to the conventional nonreciprocal circuit devices, although an attempt is made to integrate a plurality of components, preparation and assembly of many components are still required.
For example, in Japanese Unexamined Patent Application Publication No. 8-222912, although the magnetic member, the central conductor, and the permanent magnet are integrated using the integrating firing technique, the magnetic yoke must be separately prepared and be mounted on the laminate obtained using the integrating firing technique.
With respect to the lumped-constant circulator disclosed in Japanese Unexamined Patent Application Publication No. 8-330812, only the ferrimagnetic thin plates and the central conductors are integrated. That is, a permanent magnet, a magnetic yoke, etc., must be prepared as separate components, which must be assembled together with the sintered compact.
With respect to the nonreciprocal circuit device disclosed in Japanese Unexamined Patent Application Publication No. 9-326606, although the central conductor and the electrodes constituting the capacitor to be connected to the central conductor are integrally fired with the magnetic body, other components, such as a permanent magnet and a magnetic yoke, must be prepared separately and be mounted on the sintered compact.
Accordingly, the present invention resolve the several drawbacks as described above, and it is an object of the present invention to provide a nonreciprocal circuit device in which more components, including a network provided with elements such as a capacitor, can be integrated, thus efficiently improving productivity and reliability, and to provide a method of fabricating the same.
In accordance with the present invention, a nonreciprocal circuit device includes a laminated body including a magnetic substrate composed of a ferromagnetic material, a permanent-magnet substrate laminated on the magnetic substrate, a plurality of central conductors disposed on the upper surface or the lower surface of the magnetic substrate, the central conductors intersecting each other in the center while being electrically insulated from each other, and a yoke integrated into the laminated body, and a network provided within the laminated body and electrically connected to any one of the plurality of central conductors.
Preferably, the nonreciprocal circuit device further includes a dielectric substrate laminated on the magnetic substrate opposite to the permanent-magnet substrate, and the network is disposed on at least one surface of at least one of the magnetic substrate, the permanent-magnet substrate, and the dielectric substrate, and is electrically connected to any one of the central conductors.
Preferably, in the nonreciprocal circuit device, the network includes a capacitor electrode electrically connected to one end of any one of the central conductors, and a ground electrode provided on the lower surface of the laminated body. The capacitor electrode and the ground electrode constitute a capacitor.
Preferably, the yoke is constructed by a magnetic film covering the outer surface of the laminated body. Further, according to another aspect of the invention, the nonreciprocal circuit device includes a second magnetic substrate laminated on the lower surface of the laminated body, and a magnetic case coupled to the second magnetic substrate; the magnetic case covers the upper surface, the lower surface and side surfaces of the laminated body.
In accordance with the present invention, a method of fabricating the nonreciprocal circuit device includes the steps of preparing a mother magnetic substrate and a mother permanent-magnet substrate; forming an electrode for forming the network on at least one surface of at least one of the mother permanent-magnet substrate and the mother magnetic substrate; laminating the mother magnetic substrate, the mother permanent-magnet substrate, and a plurality of central conductors by an adhesive to obtain a mother laminated body; cutting the mother laminated body in the thickness direction to obtain laminated bodies corresponding to the individual nonreciprocal circuit devices; and integrating the yoke into each laminated body.